Phosphor and plasma display device

ABSTRACT

Phosphor and a plasma display device are provided whose deterioration in brightness of phosphors and a degree of change in chromaticity are alleviated and whose discharge characteristics are improved and that has excellent initial characteristics. Phosphor of the present invention is an alkaline-earth metal aluminate phosphor containing an element M (where M denotes at least one type of element selected from the group consisting of Nb, Ta, W and B). In this phosphor, a concentration of M in the vicinity of a surface of the phosphor particles is higher than the average concentration of M in the phosphor particles as a whole. A plasma display device according to the present invention includes a plasma display panel in which a plurality of discharge cells in one color or in a plurality of colors are arranged and phosphor layers are arranged so as to correspond to the discharge cells in colors and in which light is emitted by exciting the phosphor layers with ultraviolet rays. The phosphor layers include blue phosphor, where the afore-mentioned phosphor is used as the blue phosphor.

FIELD OF THE INVENTION

The present invention relates to phosphor used for a plasma displaypanel and a mercury-free discharge lamp and relates to a plasma displaydevice.

BACKGROUND OF THE INVENTION

In recent years, in the field of color display devices used forcomputers and TVs to display images, a display device employing a plasmadisplay panel (hereinafter also referred to as PDP) has receivedattention because such a device enables a large size, low profile andlight-weight color display device. A plasma display device utilizing aPDP performs full color displaying by conducting additive color mixtureof so-called three primary colors (red, green and blue). In order toperform such full color displaying, a plasma display device is providedwith phosphor layers that emit light in respective colors including red(R), green (G) and blue (B) as the three primary colors, and phosphorparticles making up these phosphor layers are excited by ultravioletrays generated in a discharge cell of a PDP so as to generate therespective colors of visible light.

As compounds used for phosphors in the respective colors, (YGd)BO₃: Eu³⁺and Y₂O₃: Eu³⁺ that emit red, Zn₂SiO₄: Mn²⁺ that emits green andBaMgAl₁₀O₁₇: Eu²⁺ that emits blue are known, for example. Thesephosphors are manufactured by mixing of prescribed raw materials,followed by baking at high temperatures of 1,000° C. or higher so as toinitiate a solid phase reaction (See Phosphors Handbook, pages 219 and225, published by Ohmsha, for example). These phosphor particlesobtained by baking are ground and screened out (the average particlediameter of red and green: 2 μm to 5 μm and the average particlediameter of blue: 3 μm to 10 μm) for the use.

The reasons for grinding and screening out (classifying) the phosphorparticles are as follows: when a phosphor layer is formed on a PDP, ageneral technique adopted is to screen-print pastes of phosphorparticles in respective colors. When applying the pastes, phosphors withsmaller and more uniform particle diameters (i.e., more uniform particlesize distribution) allow a better coated surface to be attained easily.That is, phosphors with smaller and more uniform particle diametershaving a shape closer to a sphere enable a better coated surface; theenhancement of the filling density of phosphor particles in a phosphorlayer; and an increase in light-emitting surface area of the particles.Furthermore, such phosphors can alleviate instability during addressdriving. Theoretically, it can be considered that this results from anincrease in brightness of a plasma display device.

However, when the particle diameters of the phosphor particles aredecreased, the surface area of the phosphors would increase or defectson the surface of the phosphors would increase. Therefore, the surfaceof the phosphors tends to attract a large amount of water, carbonic acidgas or hydrocarbon based organic substances. Especially, in the case ofa blue phosphor made of Ba_(1·x)MgAl₁₀O₁₇: Eu_(x) orBa_(1−x−y)Sr_(y)MgAl₁₀O₁₇: Eu_(x) (where 0.03≦X≦0.20, 0.1≦Y≦0.5) that isan alkaline-earth metal aluminate phosphor containing divalent europium(Eu) as an activator, its crystal structure has a layer structure (SeeDisplay and Imaging, 1999. Vol. 7, pp 225 to 234, for example), andoxygen (O) in the vicinity of a layer containing Ba atoms (Ba-O layer)among these layers has defects (See Applied Physics, vol. 70, No. 3,2001, p310, for example).

For that reason, water present in the air selectively is adsorbed to thesurface of the Ba-O layer of the phosphor. Therefore, a large amount ofthe water is ejected in a panel during the course of a panelmanufacturing process, and problems occur, such as deterioration inbrightness caused by the reaction with the phosphor and MgO during thedischarge (particularly, deterioration in brightness of blue and green),a change in chromaticity of the panel (shift in color caused by thechange in chromaticity and burn-in of a screen), a decrease in drivingmargin and an increase in discharge voltage. Furthermore, when vacuumultraviolet light (VUV) of 147 nm is adsorbed to the oxygen defects,another problem occurs such that the defects further increase, whichfurther increases deterioration in brightness of the phosphor. To copewith these problems, a method is proposed in which the entire surface ofthe phosphors is coated with Al₂O₃ crystals for the purpose of allowingthe defects of the conventional Ba-O layer to recover (See JP 2001-55567A, for example). However, the coating on the entire surface causes theabsorption of ultraviolet rays, which results in a problem of a decreasein brightness of light emitted from the phosphors and a problem of adecrease in brightness due to ultraviolet rays.

SUMMARY OF THE INVENTION

Therefore, with the foregoing in mind, it is an object of the presentinvention to provide a phosphor and a plasma display device whosedeterioration in brightness of phosphors and a degree of a change inchromaticity are alleviated and whose discharge characteristics areimproved and that has excellent initial characteristics.

The phosphor of the present invention is an alkaline-earth metalaluminate phosphor containing an element M (where M denotes at least onetype of element selected from the group consisting of Nb, Ta, W and B).In this phosphor, a concentration of M in the vicinity of a surface ofthe phosphor particles is higher than the average concentration of M inthe phosphor particles as a whole.

A plasma display device according to the present invention includes aplasma display panel in which a plurality of discharge cells in onecolor or in a plurality of colors are arranged and phosphor layers arearranged so as to correspond to the discharge cells in colors and inwhich light is emitted by exciting the phosphor layers with ultravioletrays. The phosphor layers include blue phosphor, the blue phosphor beingan alkaline-earth metal aluminate phosphor containing an element M(where M denotes at least one element selected from the group consistingof Nb, Ta, W and B). In this phosphor, a concentration of M in thevicinity of a surface of the phosphor particles is higher than theaverage concentration of M in the phosphor particles as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a PDP of one embodiment of the presentinvention that shows a state where a front glass substrate has beenremoved.

FIG. 2 is a perspective view showing a partial cross-section of an imagedisplay region of the PDP.

FIG. 3 is a circuit block diagram of a plasma display device of oneembodiment of the present invention.

FIG. 4 is a cross-sectional view showing a structure of an image displayregion of a PDP of one embodiment of the present invention.

FIG. 5 schematically shows a configuration of an ink applicationapparatus in cross section that is used for forming the phosphor layersof the PDP.

FIG. 6 schematically shows an atomic structure of a conventional bluephosphor.

DETAILED DESCRIPTION OF THE INVENTION

First of all, the effects obtained from the elimination of oxygendefects in the vicinity of a Ba-O layer of a blue phosphor will bedescribed below.

Phosphors used for PDPs or the like are manufactured by a solid reactionmethod, an aqueous solution reaction method and the like. In thesemethods, when a particle diameter decreases, defects become likely tooccur. Especially, in the solid reaction method, the grinding ofphosphors following the baking generates a lot of defects. Furthermore,it is known that ultraviolet rays having a wavelength of 147 nm, whichare generated from the discharge for driving a panel, also cause theoccurrence of defects in the phosphors (See Technical Report of theInstitute of Electronics, Information and Communication Engineers, EID99-94, Jan. 27, 2000, for example).

Especially, it is known that, as for BaMgAl₁₀O₁₇: Eu that is analkaline-earth metal aluminate blue phosphor, the phosphor itself hasoxygen defects, in particular in its Ba-O layer (See Applied Physics,vol. 70 No. 3, 2001, p310, for example).

FIG. 6 schematically shows a structure of the Ba-O layer of theBaMgAl₁₀O₁₇: Eu blue phosphor.

Regarding the conventional blue phosphor, it has been considered thatthe occurrence of these defects itself causes deterioration inbrightness. In other words, it has been considered that thedeterioration is caused by the defects caused by an impact on thephosphor by ions generated during the driving of a panel and the defectscaused by ultraviolet rays having a wavelength of 147 nm.

The inventors of the present invention found that the deterioration inbrightness is not caused only by the presence of such defects but theessential causes of the deterioration in brightness reside in that waterand carbonic acid gas or hydrocarbon gas selectively are adsorbed to theoxygen (O) defects in the vicinity of a Ba-O layer and vacuumultraviolet light (VUV) and ions are applied to the adsorbed state, thusresulting in a reaction of the phosphor with water so as to generatedeterioration in brightness and shift in color. That is to say, theinventors of the present invention found that a large amount of waterand carbonic acid gas or hydrocarbon gas are adsorbed to the oxygendefects in the vicinity of the Ba-O layer of the blue phosphor, and theadsorbed water and carbonic acid gas or hydrocarbon diffuse into thepanel during the discharge, thus causing not only the deterioration inblue but also the deterioration in green.

From these findings, by decreasing the oxygen defects in the vicinity ofthe Ba-O layer of the blue phosphor, the amount of absorption of thewater and the carbonic acid gas or the hydrocarbon gas to the bluephosphor could be decreased significantly and deterioration in thebrightness of blue and green during the manufacturing of a panel andduring the driving of the panel could be avoided, whereby a plasmadisplay device free from uneven color and burn-in of a screen and havinga long life could be obtained. That is, in order to decrease the oxygendefects in the vicinity of the Ba-O layer, a part of aluminum (Al),magnesium (Mg) and barium (Ba) elements of the blue phosphor having acrystal structure of Ba_(1·x)MgAl₁₀O₁₇: Eu_(x) orBa_(1−x−y)Sr_(y)MgAl₁₀O₁₇: Eu_(x) (where 0.03≦X≦0.20, 0.1≦Y≦0.5) issubstituted with elements (Nb, Ta, W, B) or is arranged in the vicinityof these ions and elements. Thereby, the oxygen defects in the vicinityof the Ba-O layer could be decreased.

The following describes the effects of substituting positive ions in theBa_(1·x)MgAl₁₀O₁₇ (where 0.03≦X≦0.20) with the specific elements (Nb,Ta, W, B) added thereto.

Al, Mg and Ba in the Ba_(1·x)MgAl₁₀O₁₇: Eu_(x) (where 0.03≦X≦0.20) asthe blue phosphor are present as trivalent (Al) or divalent (Mg, Ba)plus ions. At a position of any one of these ions or in the vicinity ofthem, at least one element or ion selected from the group consisting ofNb, Ta, W and B, which are present mainly as positive ions, are allowedto be located, whereby positive electrical charge increases more in thecrystals than from the conventional one. Conceivably, in order toneutralize such positive (+) electrical discharge (i.e., to compensatefor the electrical charge), oxygen having negative electrical chargefills in an oxygen defect in the vicinity of a Ba element, which resultsin a decrease in oxygen defects in the vicinity of the Ba-O layer. Thatis, the specific trivalent to quinquevalent elements allow thecompensation for oxygen defects with efficiency, because these elementshave the capability of attracting a larger amount of oxygen. Among theelements such as Cr, Se, Te, Mo, W and Re, it was found that theaddition of Nb, Ta, W and B selectively allows a particular largereffect to be attained.

As a method for manufacturing phosphors, a solid phase sintering method,a liquid phase method and a liquid spraying method are available. In thesolid phase sintering method, conventional oxides and nitrate orcarbonate materials and a flux are used. In the liquid phase method, anorganic metal salt and nitrate are used, and these are hydrolyzed in anaqueous solution or are precipitated by adding an alkali or the likeusing a coprecipitation method so as to form a precursor of thephosphor, followed by a heat treatment applied thereto. In the liquidspraying method, an aqueous solution containing a raw material forphosphor is sprayed in a heated oven so as to manufacture the phosphor.According to any one of these methods, it was found that the effects canbe obtained by substituting a part of Al, Mg and Ba elements inBa_(1·x)MgAl₁₀O₁₇: Eu_(x) (where 0.03≦X≦0.20) with the specific elements(Nb, Ta, W and B).

According to the present invention, Mg, Al and Ba elements in crystalsof blue phosphor that is an alkaline-earth metal aluminate phosphor aresubstituted with at least one type of element selected from the groupconsisting of Nb, Ta, W and B. Thereby, oxygen defects in the bluephosphor can be reduced, deterioration in brightness during the varioussteps for the phosphor layer can be avoided, and deterioration inbrightness and change in chromaticity of the panel can be alleviated anddischarge characteristics can be improved. As a result, a plasma displaydevice that allows address errors of the panel to be avoided, enables areduction in uneven color and shift in color and has excellent initialcharacteristics and high reliability can be realized.

Firstly, as one example of a method for manufacturing phosphor, a methodusing the solid reaction method for a blue phosphor will be describedbelow. As raw materials, carbonates and oxides such as BaCO₃, MgCO₃,Al₂O₃, Eu₂O₃, MO₃ (where M denotes Nb, Ta, W and B) are used, to which asmall amount of a flux (AlF₃, BaCl₂) is added as an accelerating agentfor sintering, followed by baking at 1400° C. for 2 hours. Thereafter,the resultant is ground and screened out, and then is baked at 1500° C.for 2 hours in a reducing atmosphere (H₂ 25 vol %, N₂ 75 vol %). Then,the resultant is ground and screened out again so as to obtain thephosphor. Next, in order to further decrease the defects of the phosphormanufactured by the reducing procedure, the resultant is annealed in anoxidizing atmosphere at a temperature so as not to cause resintering ofthe phosphor, whereby the blue phosphor is obtained.

According to the liquid phase method in which phosphor is manufacturedfrom an aqueous solution, an organic metal salt containing elementsconstituting the phosphor such as alkoxide and acetylacetone or nitrateis dissolved in water, and the resultant is hydrolyzed so as tomanufacture a coprecipitate (hydrate). The coprecipitate (hydrate)undergoes hydrothermal synthesis (crystallization in an autoclave), isbaked in the air or is sprayed in an oven at a high temperature so as toobtain powder. The thus obtained powder is baked at 1500° C. for 2 hoursin a reducing atmosphere (H₂ 25 vol %, N₂ 75 vol %) so as to obtain aphosphor. The blue phosphor obtained by the above-stated method isground and is screened out, and then is annealed in an oxidizingatmosphere at a temperature so as not to cause resintering of thephosphor, whereby the phosphor is obtained.

The amount of specific elements (Nb, Ta, W, B), with which Al, Mg and Baare substituted, preferably is within a range of 0.001 mol % to 3 mol %,inclusive, with reference to Al, Mg and Ba. In the case of thesubstitution amount less than 0.001 mol %, the effects for avoidingdeterioration in brightness is small and in the case of the substitutionamount more than 3 mol %, the brightness of the phosphor tends todecrease.

In this way, the conventional methods for manufacturing blue phosphorpowder are used, and Al, Mg and Ba ions in the Ba_(1·x)MgAl₁₀O₁₇: Eu_(x)(where 0.03≦X≦0.20) crystal are substituted with the specific ions orelements (Nb, Ta, W, B), whereby a phosphor resistant to water andvacuum ultraviolet light (VUV), which means to have a durability againstwater and carbonic acid gas generated during a phosphor baking process,a panel sealing process, a panel aging process or during the driving ofa panel, can be obtained without a decrease in brightness of bluephosphors and green phosphors.

In this way, a plasma display device according to the present inventionhas a configuration including a PDP in which a plurality of dischargecells in one color or in a plurality of colors are arranged and phosphorlayers are arranged so as to correspond to the discharge cells in colorsand in which light is emitted by exciting the phosphor layers withultraviolet rays. In this PDP, a blue phosphor layer is composed of bluephosphors in which Al, Mg and Ba ions in Ba_(1·x)MgAl₁₀O₁₇: Eu_(x) orBa_(1−x−y)Sr_(y)MgAl₁₀O₁₇: Eu_(x) (where 0.03≦X≦0.20, 0.1≦Y≦0.5) crystalhaving a uniform particle size distribution are substituted with thespecific ions (Nb, Ta, W, B).

Then, the particle diameter of the blue phosphor particles, in which apart of Al or Mg ions in Ba_(1·x)MgAl₁₀O₁₇: Eu_(x) orBa_(1−x−y)Sr_(y)MgAl₁₀O₁₇: Eu_(x) (where 0.03≦X≦0.20, 0.1≦Y≦0.5) issubstituted with ions (Nb, Ta, W, B), is as small as 0.05 μm to 3 μm andits particle size distribution is excellent. Furthermore, if the shapeof the phosphor particles making up a phosphor layer is spherical, afilling density further is improved, which leads to a substantialincrease in light-emitting area of the phosphor particles thatcontribute to the light-emission. As a result, the brightness of aplasma display device is enhanced, and at the same time deterioration inbrightness and shift in color are suppressed, so that the plasma displaywith excellent brightness characteristics can be obtained.

The afore-mentioned blue phosphor particles include an alkaline-earthmetal aluminate phosphor containing tungsten (W), and it is preferablethat a concentration of tungsten (W) in the vicinity of a surface of thephosphor particles is higher than the average concentration of tungsten(W) in the phosphor particles as a whole.

In the present invention, preferably, the afore-mentioned alkaline-earthmetal aluminate includes an alkaline-earth metal aluminate representedby the general formula of xBaO.(1·x)SrO.zMgO.5Al₂O₃ (0.60≦x≦1.00,1.00≦z≦1.05), and contains 0.40 to 1.70 mol % of Eu oxide in terms of Euand contains 0.04 to 0.80 mol % of W oxide in terms of W with referenceto the afore-mentioned alkaline-earth metal aluminate.

Furthermore, it is preferable that the concentration of W in thevicinity of the surface of the phosphor particles ranges from 0.30 to9.00 mol %.

Furthermore, it is preferable that the concentration of Eu in thevicinity of the surface of the phosphor particles is higher than theaverage concentration of Eu in the phosphor particles as a whole, andthe divalent Eu ratio (the ratio of divalent Eu elements to all of theEu elements) in the vicinity of the surface of the phosphor particles islower than the average divalent Eu ratio in the phosphor particles as awhole.

Furthermore, it is preferable that the divalent Eu ratio in the vicinityof the surface of the phosphor particles ranges from 5 to 50 mol % andthe average divalent Eu ratio in the phosphor particles as a wholeranges from 60 to 95 mol %.

Furthermore, it is preferable that the divalent Eu ratio in the vicinityof the surface of the phosphor particles ranges from 5 to 15 mol % andthe average divalent Eu ratio in the phosphor particles as a wholeranges from 60 to 80 mol %.

The following describes a method for manufacturing a plasma displaydevice of the present invention. This manufacturing method includes thesteps of: an arrangement process in which pastes are arranged indischarge cells of a rear panel (rear substrate) described later, thepastes including phosphor particles for blue phosphor in which Al, Mg orBa ions in Ba_(1·x)MgAl₁₀O₁₇: Eu_(x) or Ba_(1−x−y)Sr_(y)MgAl₁₀O₁₇:Eu_(x) (where 0.03≦X≦0.20, 0.1≦Y≦0.5) are substituted with ions (Nb, Ta,W, B), red and green phosphor particles and a binder; a baking processfor burning the binder included in the paste arranged on the rear panelto dissipate the same, and a process for overlaying the rear panel, onwhich phosphor particles are arranged on the substrate by the bakingprocess, on a front panel described later.

Note here that a more preferable average particle diameter of thephosphor particles is within a range of 0.1 μm to 2.0 μm. Furthermore,as for a particle size distribution, it is more preferable that themaximum particle size is not more than four times the average value andthe minimum value is not less than one-fourth of the average value. Thisis because a region where ultraviolet rays can reach in the phosphorparticles is as shallow as several hundred nm from the surface of theparticles, and only a portion near to the surface contributes to thelight-emission. When the particle diameter of such phosphor particles iskept at 2.0 μm or less, a surface area of the particles contributing tothe light-emission increases, so that the luminescent efficiency of thephosphor layer can be kept in a high state. When the particle diameterexceeds 3.0 μm, the phosphor layer is required to have a thickness of 20μm or more, and therefore it becomes difficult to secure the sufficientdischarge space. When the particle diameter is less than 0.05 μm, thedefects become likely to occur, and it becomes difficult to enhance thebrightness. When the thickness of the phosphor layer is within a rangeof eight to twenty-five times the average particle diameter of thephosphor particles, the discharge space can be secured sufficientlywhile keeping the luminescent efficiency of the phosphors layer in ahigh state, and therefore the brightness of the plasma display devicecan be increased.

Furthermore, in the phosphor of the present invention, it is preferablethat the concentration of M (Nb, Ta, W, B) in the vicinity of thesurface of the phosphor particles is higher than the averageconcentration of M in the phosphor particles as a whole. With thisphosphor, deterioration in light-emission intensity and change inchromaticity, caused by the irradiation with vacuum ultraviolet lightand heat, can be reduced. More specifically, it is more preferable thatthe concentration of element M in the vicinity of the surface of thephosphor particles is twice or higher the average concentration in thephosphor particles as a whole, particularly preferably three times orhigher.

It is preferable that the concentration of M in the vicinity of thesurface of the particle diameters is higher than the averageconcentration of M in the phosphor particles as a whole, and that thecontent ratio to the alkaline-earth metal aluminate (preferably, thecontent ratio to the alkaline-earth metal aluminate represented by theafore-mentioned general formula) ranges from 0.30 to 9.00 mol %.Although the concentration of M in the vicinity of the surface of thephosphor particles should be higher than the average concentration of Min the phosphor particles as a whole, preferably, the former is higherthan the latter by a range from 0.26 to 8.20 mol %.

Note here that for the purposes of the present invention, the vicinityof the surface of the phosphor particles means a region where thephosphor is excited by a short-wavelength light such as vacuumultraviolet light so as to emit light, more specifically refers to theregion of 50 nm from the surface of the phosphor particles. Morepreferably, this may refer to the average value of the region of 10 nmfrom the surface of the phosphor particles. Herein, since the depth ofthe excited light entering into the phosphor varies with the wavelengthof the light, the above numerical example is not a limiting one.

In order to make the concentration of M (Nb, Ta, W, B) in the vicinityof the surface of the phosphor particles higher than the averageconcentration of M (Nb, Ta, W, B) in the phosphor particles as a whole,a preferable method is to control the atmosphere and the temperature ofthe baking step of the phosphor. More specifically, the baking stepincludes: a first step in which the mixed powder of raw materials of thephosphor or the powder baked in the air is baked in a reducingatmosphere; and a second step in which, at the fall in temperature ofthe first step or after that, a heat treatment is conducted in an inertatmosphere.

One example of a method for manufacturing such a phosphor will bedescribed below.

As starting materials, BaCO₃, SrCO₃, MgO, Al₂O₃, EuF₃, Nb₂O₅, Ta₂O₅, WO₃and Ba₂O₃ were used. They were weighed so as to have a predeterminedcomposition, and were subjected to wet blending in pure water using aball mill. After drying this mixture, this was subjected to reductionbaking at 1200 to 1500° C. for 4 hours in a mixed gas of nitrogen andhydrogen corresponding to a reducing atmosphere (as one example, amixture gas of 96 vol % of nitrogen and 4 vol % of hydrogen), and thetemperature was allowed to fall from the baking temperature to 1000° C.in nitrogen corresponding to an inert atmosphere, and further was cooleddown to a room temperature in a mixed gas of nitrogen and oxygencorresponding to an oxidizing atmosphere (as one example, a mixture gasof 98 vol % of nitrogen and 2 vol % of oxygen), thus obtaining phosphor.In this way, by changing the baking temperatures and the atmosphereduring the step of the fall in temperature, the concentrationdistribution of M, the concentration distribution of Eu and the divalentEu ratio in the phosphor particles were controlled.

The concentration of M (the surface M concentration), the concentrationof Eu (the surface Eu concentration) and the divalent Eu ratio (thesurface divalent Eu ratio) in the vicinity of the phosphor particleswere measured by X-ray photoelectron spectroscopy (XPS). In the surfaceanalysis by XPS, the average value of the elements residing at a regionof 10 nm from the surface of the phosphor was measured. The averageconcentration of M (average M concentration), the average concentrationof Eu (average Eu concentration) and the average divalent Eu ratio ofthe phosphor particles as a whole were measured by a fluorescent X-raymethod.

Table 1 shows the composition ratio, the concentrations of therespective elements (the average M concentration, the average Euconcentration, the average divalent Eu ratio, the surface Mconcentration, the surface Eu concentration and the surface divalent Euratio) and the maintenance factor of the light-emission intensity of thesamples Y/y after the irradiation with vacuum ultraviolet light having awavelength of 146 nm for 100 hours (i.e., the ratio of thelight-emission intensity after the irradiation to the initiallight-emission intensity value) of the thus manufactured phosphors. Notehere that Y and y denote the brightness Y and the chromaticity y thatcomply with the XYZ colorimetric system of the International Commissionon Illumination, and the light-emission intensity Y/y represents arelative value. In Table 1, the sample to which a * mark is given is acomparative example.

X and z denote the values of x and z in the general formula of xBaO(1·x)SrO.zMgO.5Al₂O₃. TABLE 1 Average Surface Y/y compositioncomposition Mainte- divalent divalent nance Sample M Eu Eu M Eu Eufactor No. x z M (mol %) (mol %) (mol %) (mol %) (mol %) (mol %) (%) *10.90 0.90 none 0 0.83 90 0 0.83 90 35 *2 0.90 0.90 Nb 0.02 0.83 86 0.020.83 83 48 3 0.60 1.00 Nb 0.04 0.40 80 0.12 1.20 50 82 4 1.00 1.05 Ta0.04 1.70 75 0.25 8.50 45 80 5 0.85 1.00 W 0.80 0.80 62 9.00 5.60 15 966 0.85 1.00 B 0.04 0.80 73 0.30 4.00 30 90 7 0.85 1.00 W 0.10 0.80 601.00 7.00 18 97 8 0.85 1.00 W½B½ 0.10 0.80 68 1.00 6.40 23 99 9 0.851.00 W 0.10 0.80 95 0.85 6.70 50 90 10 0.85 1.00 W 0.10 0.80 80 1.006.00 15 95 11 0.85 1.00 W 0.10 0.80 60 1.00 7.50 5 99 12 0.60 1.00 W0.04 0.40 80 0.12 1.20 50 85 13 1.00 1.05 W 0.04 1.70 75 0.25 8.50 45 8714 0.85 1.00 W 0.04 0.80 73 0.30 4.00 30 94 15 0.85 1.00 Ta 0.04 0.80 7512.00 3.30 13 75 16 0.90 1.00 W 0.04 0.80 75 0.30 4.00 35 93 17 0.901.00 W 0.20 0.80 80 1.20 7.20 22 95 18 0.90 1.00 W 0.80 0.80 71 9.006.10 19 97 19 0.90 1.00 Nb 0.04 0.80 73 0.30 3.80 37 94 20 0.90 1.00 Nb0.20 0.80 78 1.20 6.50 27 96 21 0.90 1.00 Nb 0.80 0.80 69 9.00 5.60 2597 22 0.90 1.00 Ta 0.04 0.80 72 0.30 3.90 24 90 23 0.90 1.00 Ta 0.200.80 80 1.20 7.00 25 91 24 0.90 1.00 Ta 0.80 0.80 66 9.00 5.80 22 92 250.90 1.00 W½Nb½ 0.04 0.80 73 0.30 4.10 34 95 26 0.90 1.00 W½Nb½ 0.200.80 81 1.20 7.30 23 96 27 0.90 1.00 W½Nb½ 0.20 0.80 69 9.00 5.70 20 97(Remark)*1, *2 represent comparative examples.

As is evident from Table 1, the phosphors according to the presentinvention are reduced in the deterioration in light-emission intensitycaused by the irradiation with vacuum ultraviolet light. Furthermore,the samples whose surface M concentrations range from 0.30 to 9.00 mol %especially are reduced in the deterioration.

The samples 2 to 11 were kept in the air at 500° C. for 1 hour, andchanges in light-emission intensity and chromaticity before and afterthe heat treatment were determined. As a result, both of thelight-emission intensity and the chromaticity of sample 2 significantlychanged, whereas the light-emission intensities and the chromaticitiesof samples 3 to 11 were much the same as those before the heattreatment. In particular, the light-emission intensities of the sampleshaving the surface divalent Eu ratio of 5 to 50 mol % and having theaverage divalent Eu ratio of 60 to 95 mol % did not change at all, andmoreover the samples having the surface divalent Eu ratio of 5 to 15 mol% and having the average divalent Eu ratio of 60 to 80 mol % did notchange in their chromaticities at all also.

Furthermore, in the present invention, the following optimum combinationof the phosphors allows a plasma display device free from a change inchromaticity (shift in color and burn-in) and deterioration inbrightness to be attained.

As the optimum phosphor particles used for a blue phosphor layer, acompound represented by Ba_(1·x)MgAl₁₀O₁₇: Eu_(x) orBa_(1−x−y)Sr_(y)MgAl₁₀O₁₇: Eu_(x) to which the specific ions or elements(Nb, Ta, W, B) are added may be used. Herein, it is preferable the valueof x in the compound is 0.03≦X≦0.20 and the value of y is 0.1≦Y≦0.5,because high brightness can be realized.

As preferable phosphor particles used for a red phosphor layer, acompound represented by Y_(2−x)O₃: Eu_(x) or (Y, Gd)_(1−x)BO₃: Eu_(x) ora mixture of these may be used. Herein, it is preferable that the valueof x in the compound for a red phosphor is 0.05≦X≦0.20, because theexcellent effects concerning brightness and against deterioration inbrightness can be obtained.

As preferable phosphor particles used for a green phosphor layer, acompound represented by Y_(1−x)BO₃: Tb_(x) or Zn_(2−x)SiO₄: Mn_(x) or amixture of these may be used. Herein, it is preferable that the value ofx in the compound for a green phosphor is 0.01≦X≦0.10, because theexcellent effects concerning brightness and against deterioration inbrightness can be obtained.

The following describes a plasma display device according to oneembodiment of the present invention, with reference to the drawings.

FIG. 1 is a schematic plan view of a PDP that shows a state where afront glass substrate has been removed, and FIG. 2 is a perspective viewshowing a partial cross-section of an image display region of the PDP.Note here that, in FIG. 1, a display electrode group, a display scanningelectrode group and an address electrode group are illustrated bypartially omitting the same for the sake of intelligibility. Referringnow to FIG. 1 and FIG. 2, a structure of the PDP will be describedbelow.

As shown in FIG. 1, a PDP 100 includes a front glass substrate (notillustrated), a rear glass substrate 102, N pieces of display electrodes103, N pieces of display scanning electrodes 104 (the N-th electrode isprovided with its number), M pieces of address electrodes group 107 (theM-th electrode is provided with its number), a hermetically sealinglayer 121 and the like. The PDP 100 has a matrix of electrodes having athree-electrode structure made up of the respective electrodes 103, 104and 107, and cells are formed at intersection points of the respectivedisplay scanning electrodes 104 and address electrodes 107. Referencenumeral 122 denotes a discharge space and 123 denotes an image displayregion.

As shown in FIG. 2, this PDP 100 is configured by bonding the frontpanel with the rear panel and by filling the discharge space 122 formedbetween the front panel and the rear panel with a discharge gas, wherethe front panel includes the display electrode group 103, the displayscanning electrode group 104, a dielectric glass layer 105 and a MgOprotective layer 106 provided on one major surface of a front glasssubstrate 101. The rear panel includes the address electrodes 107, adielectric glass layer 108, barrier ribs 109, a phosphor layer 110R (redphosphor), a phosphor layer 110G (green phosphor) and a phosphor layer110B (blue phosphor) are provided on one major surface of a rear glasssubstrate 102. The arrow of FIG. 2 indicates a direction of displayingan image.

When the plasma display device is driven for displaying, as shown inFIG. 3, a display driver circuit 153, a display scanning driver circuit154, an address driver circuit 155 are connected with the PDP. Then, inaccordance with the control signal from a controller 152, a signalvoltage is applied to a discharge cell to be illuminated by way of thedisplay scanning electrode 104 and the address electrode 107, andaddress discharge is conducted within the discharge cell. Thereafter, apulse voltage is applied between the display electrode 103 and thedisplay scanning electrode 104 so as to conduct sustain discharge. Thissustain discharge enables the generation of ultraviolet rays in thedischarge cell, and the phosphor layer excited by the ultraviolet raysemits light, so that the discharge cell illuminates. The combination ofilluminated and not-illuminated discharge cells in respective colorsallows an image to be displayed.

The following describes a method for manufacturing the above-describedPDP 100, with reference to FIG. 4 and FIG. 5.

The front panel is manufactured as follows: firstly, N pieces of displayelectrodes 103 and N pieces of display scanning electrodes 104 (although2 pieces for each only are illustrated in FIG. 2) are formed alternatelyand in parallel with each other on the front glass substrate 101 so asto form stripes, and then this is coated with a dielectric glass layer105, and on the surface of the dielectric glass layer 105, a MgOprotective layer 106 further is formed.

The display electrodes 103 and the display scanning electrode 104 areelectrodes made of silver, which are formed by applying a silver pastefor electrodes by screen-printing, followed by baking.

The dielectric glass layer 105 is formed as follows: a paste containinga lead-based glass material is applied by screen-printing, followed bybaking at a predetermined temperature for a predetermined time period(e.g., at 560° C. for 20 minutes), so as to have a predeterminedthickness (about 20 μm). As the above paste containing a lead-basedglass material, a mixture of PbO (70 wt %), B₂₀₃ (15 wt %), SiO₂ (10 wt%) and Al₂O₃ (5 wt %) and an organic binder (10 wt % of ethylcellulosedissolved in α-terpinenol) may be used, for example. Herein, the organicbinder refers to a resin dissolved in an organic solvent, and acrylicresin may be used as the resin in addition to the ethylcellulose andbutyl carbitol may be used as the organic solvent. Moreover, adispersing agent (e.g., glycerol trioleate) may be mixed with such anorganic binder.

The MgO protective layer 106 is made of magnesium oxide (MgO), which isformed by sputtering or CVD (chemical vapor deposition), for example, soas to have a predetermined thickness (about 0.5 μm).

The rear panel is formed as follows: firstly, a silver paste forelectrodes is screen-printed on the rear glass substrate 102, followedby baking so that M pieces of address electrodes 107 are formed so as tobe arranged in the column direction. A paste containing a lead-basedglass material is applied thereon by screen-printing so as to form adielectric glass layer 108, and similarly a paste containing alead-based glass material is applied thereon by screen-printingrepeatedly at predetermined intervals, followed by baking, so as to formthe barrier ribs 109. The discharge space 122 is divided into eachdischarge cell (unit luminescent area) in the line direction by thesebarrier ribs 109.

FIG. 4 is a cross-sectional view showing a part of the PDP 100. As shownin FIG. 4, an interval dimension W between the barrier ribs 109 (a widthof one discharge cell) is specified as about 130 μm to 240 μm. This is ageneral specification for HD-TVs (high definition TVs) of 32-inch to50-inch in size. Phosphor inks in a paste form are applied in groovesbetween the rib walls 109. The phosphor inks include: the phosphorparticles in respective colors for red (R), green (G) and blue (B) inwhich Al, Mg or Ba element ions in Ba_(1·x)MgAl₁₀O₁₇: Eu_(x) orBa_(1−x−y)Sr_(y)MgAl₁₀O₁₇: Eu_(x) are substituted with ions or elements(Nb, Ta, W, B); and an organic binder. This is baked at a temperature of400 to 590° C. so as to burn and dissipate the organic binder, wherebyphosphor layers 110R, 110G and 110B are formed in which the respectivephosphor particles are bound with each other.

The thickness L of these phosphor layers 110R, 110G and 110B in thelamination direction on the address electrodes 107 preferably is abouteight to twenty-five times the average particle diameters of thephosphor particles in the respective colors. That is, in order to securethe brightness (luminescent efficiency) when these phosphor layers areirradiated with certain intensity of ultraviolet rays, the phosphorlayers need to have capability of absorbing ultraviolet rays generatedwithin the discharge space without letting the ultraviolet rays passtherethrough, and therefore the thickness corresponding to thelamination of eight layers of the phosphor particles at minimum ispreferable, more preferable is a thickness corresponding to twentylayers of the phosphor particles. When exceeding the thicknesscorresponding to the twenty layered lamination of phosphor particles,the luminescent efficiency of the phosphor layers becomes saturated, anda sufficient size for the discharge space 122 cannot be secured.

Furthermore, in the case of phosphor particles obtained by ahydrothermal synthesis method or the like, the particle diameter thereofis sufficiently small and the particles are spherical. Therefore, ascompared with the case using the particles that are not spherical, thefilling density of the phosphor layer can be enhanced even from the samelamination number and a total surface area of the phosphor particlesincreases, thus increasing a surface area of the phosphor particlescontributing to the actual luminescence in the phosphor layer andfurther enhancing the luminescent efficiency.

A method for synthesizing these phosphor layers 110R, 110G and 110B anda method for manufacturing blue phosphor particles used for a bluephosphor layer in which substitution with the specific ions (Nb, Ta, W,B) is conducted will be described later.

The thus manufactured front panel and rear panel are overlaid so thatthe respective electrodes on the front panel are orthogonal to theaddress electrodes on the rear panel, and a sealing glass is insertedtherebetween along the edge of the panel. This is baked at about 450° C.for 10 to 20 minutes, for example, so as to form a hermetically sealedlayer 121 (FIG. 1) for sealing. Then, after the discharge space 122 isfirst evacuated to high vacuum (e.g., 1.1×10⁻⁴ Pa), the space is filledwith a discharge gas (e.g., He—Xe based, Ne—Xe based inert gas) under apredetermined pressure so as to manufacture the PDP 100.

FIG. 5 schematically shows a configuration of an ink applicationapparatus 20 used for forming the phosphor layers 110R, 110G and 110B.

As shown in FIG. 5, the ink application apparatus 200 is provided with asupply container 210, a booster pump 220, a header 230 and the like. Apressure is applied by the booster pump 220 to a phosphor ink suppliedfrom the supply container 210 containing the phosphor ink so as tosupply the phosphor ink to the header 230. The header 230 is providedwith an ink space 230 a and a nozzle 240, and the phosphor ink suppliedto the ink space 230 a under the pressure is dispensed continuously fromthe nozzle 240. Preferably, a diameter of the hole of this nozzle 240 is30 μm or more so as to avoid the clogging of the nozzle and is not morethan the interval W (about 130 μm to 200 μm) between the barrier ribs109 for avoiding run-off beyond the barrier rib during the application.It generally is set at 30 μm to 130 μm.

The header 230 is configured so as to be linearly driven by a headerscanning mechanism (not illustrated). While scanning the header 230, aphosphor ink 250 is dispensed continuously from the nozzle 240, wherebythe phosphor ink can be applied uniformly into the groove between thebarrier ribs 109 on the rear glass substrate 102. Herein, the viscosityof the phosphor ink used is kept in a range of 1500 to 30000 CP at 25°C.

The supply container 210 is provided with a stirrer (not illustrated)and the precipitation of the particles in the phosphor ink can beavoided by the stirring. The header 230 is molded integrally with theink space 230 a and the nozzle 240 and is manufactured by machineryprocessing or electrical discharge machining of a metal material.

The method for forming the phosphor layer is not limited to the above,and various methods are available including a photo lithography method,a screen printing method, a method for arranging a film in whichphosphor particles are mixed and the like.

The phosphor ink is prepared by mixing phosphor particles of therespective colors, a binder and a solvent so as to have 1500 to 30000centi-poise (CP). A surface-active agent, silica, a dispersing agent(0.1 to 5 wt %) and the like may be added thereto, as needed.

As red phosphor mixed in the phosphor ink, a compound represented by (Y,Gd)_(1−x)BO₃: Eu_(x) or Y_(2−x)O₃: Eu_(x) may be used. This is acompound in which a part of Y elements making up its matrix material issubstituted with Eu. Herein, the substitution amount X of Eu elementswith reference to Y elements preferably is within a range of0.05≦X≦0.20. When the substitution amount exceeds this range, althoughthe brightness increases, deterioration in brightness becomesremarkable, and therefore it becomes difficult to use practically it,conceivably. On the other hand, when the substitution amount is belowthis range, the composition ratio of Eu as the luminescent centerdecreases, thus decreasing the brightness, and therefore the use as thephosphor becomes impossible.

As a green phosphor, a compound represented by Zn_(2−x)SiO₄: Mn_(x) orY_(1−x)BO₃: Tb_(x) may be used. Zn_(2−x)SiO₄: Mn_(x) is a compound inwhich a part of Zn elements making up its matrix material is substitutedwith Mn. Y_(1−x)BO₃: Th_(x) is a compound in which a part of Y elementsmaking up its matrix material is substituted with Tb elements. Herein,the substitution amount X of Mn elements with reference to Zn elementspreferably is within a range of 0.01≦X≦0.10 for the same reasonsdescribed for the red phosphor. The substitution amount X of Th elementswith reference to Y elements preferably is within a range of0.02≦X≦0.15.

As a blue phosphor, a compound represented by Ba_(1·)MgAl₁₀O₁₇: Eu_(x)or Ba_(1−x−y)Sr_(y)MgAl₁₀O₁₇: Eu_(x) (where 0.03≦X≦0.20, 0.1≦Y≦0.5) maybe used. Ba_(1·x)MgAl₁₀O₁₇: Eu_(x) or Ba_(1−x−y)Sr_(y)MgAl₁₀O₁₇: Eu_(x)(where 0.03≦X≦0.20, 0.1≦Y≦0.5) is a compound in which a part of Baelements making up its matrix material is substituted with Eu or Sr.

The substitution amount of ions or elements (Nb, Ta, W, B), with whichAl, Mg and Ba element ions are substituted, preferably ranges from 0.001mol % to 3 mol %.

As the binder mixed in the phosphor ink, ethylcellulose and acrylicresin may be used (mixed at 0.1 to 10 wt % of the ink), and as thesolvent, a-terpinenol and butyl carbitol may be used. As the binder, apolymer such as polymethyl methacrylate (PMA) and polyvinyl acetate(PVA) and an organic solvent such as diethylene glycol and methyl ethermay be used.

Furthermore, in the present embodiment, phosphor particles manufacturedby a solid phase sintering method, an aqueous solution method and aspraying and baking method and a hydrothermal synthesis method may beused, which will be described below in detail.

(1) Blue Phosphor (Ba_(1·x)MgAl₁₀O₁₇: Eu_(x))

Firstly, in a step of manufacturing a mixture solution, barium nitrateBa(NO₃)₂, magnesium nitrate Mg(NO₃)₂, aluminum nitrate Al(NO₃)₃ andeuropium nitrate Eu(NO₃)₂ as raw materials are mixed so as to have amolar ratio of 1−X:1:10: X (0.03≦X≦0.20). This is dissolved in anaqueous medium so as to manufacture a mixture solution. As this aqueousmedium, ion-exchanged water and pure water are preferable because theydo not contain impurities, but they may contain a non-aqueous medium(methanol and ethanol).

As raw materials for substituting Mg, Al and Ba with ions (Nb, Ta, W,B), nitrates, chlorides and organic compounds of the above ions (Nb, Ta,W, B) may be used. The substitution amount of the ions or elements (Nb,Ta, W, B) with which Al, Mg and Ba element ions are substitutedpreferably is within a range of 0.001 mol % to 3 mol %.

Next, the hydrate mixture solution is poured into a container havingcorrosion and heat resistance, made of gold or platinum, for example,which is then subjected to hydrothermal synthesis (for 12 to 20 hours)in a high pressure container at a predetermined temperature (100 to 300°C.) and under a predetermined pressure (0.2 MPa to 10 MPa) using anapparatus such as an autoclave enabling the application of heat andpressure.

Next, the resulting powder is baked at a predetermined temperature andfor a predetermined time period, e.g., at 1350° C. for 2 hours in areducing atmosphere containing 5% of hydrogen and 95% of nitrogen, forexample. Thereafter, this is screened out, whereby desired blue phosphorBa_(1·x)MgAl₁₀O₁₇: Eu_(x) in which a part of Mg, Al and Ba issubstituted with ions (Nb, Ta, W, B) can be obtained. Moreover, in orderto enhance the resistance to vacuum ultraviolet light (VUV), the abovephosphor is baked in an oxidizing atmosphere (preferably, 700° C. to1000° C.).

The phosphor particles obtained by conducting the hydrothermal synthesishave a spherical shape, whose average particle diameter becomes about0.05 μm to 2.0 μm. A smaller particle diameter can be formed as comparedwith the conventional particles manufactured by solid phase reaction.Note here that the “spherical” in this context is defined in a mannerthat the aspect ratio (diameter in minor axis/diameter in major axis)ranges from 0.9 to 1.0, inclusive. However, all of the phosphorparticles are not necessarily within this range. In other words, variousparticle shapes may be included.

Furthermore, without putting the above hydrate mixture solution in thecontainer made of gold or platinum, the blue phosphor can bemanufactured by a spraying method in which this hydrate mixture solutionis sprayed into a high temperature oven from a nozzle so as tosynthesize the phosphor.

(2) Blue Phosphor (Ba_(1−x−y)Sr_(y)MgAl₁₀O₁₇: Eu_(x))

This phosphor (x and y are the same as above) is different from theafore-mentioned Ba_(1·x)MgAl₁₀O₁₇: Eu_(x) only in the raw materials, andis manufactured by a solid phase reaction method. The followingdescribes the raw materials used.

As the raw materials, barium hydroxide Ba(OH)₂, strontium hydroxideSr(OH)₂, magnesium hydroxide Mg(OH)₂, aluminum hydroxide Al(OH)₃ andeuropium hydroxide Eu(OH)₂ are weighed to have a required molar ratioand then oxides and hydroxides of the specific ions (Nb, Ta, W, B) withwhich Mg, Al and Ba are substituted are weighed so as to have a requiredratio. These are mixed with AlF₃ as a flux, followed by baking at apredetermined temperature (1300° C. to 1400° C.) for 12 to 20 hours,whereby Ba_(1−x−y)Sr_(y)MgAl₁₀O₁₇: Eu_(x) in which Mg and Al have beensubstituted with the specific ions (Nb, Ta, W, B) can be obtained. Theaverage particle diameter of the phosphor particles obtained by thismethod is about 0.1 μm to 3.0 μm.

Next, this is baked at a predetermined temperature (1000° C. to 1600°C.) for 2 hours in a reducing atmosphere of 5% of hydrogen and 95% ofnitrogen, for example, and then is screened out by an air classifier soas to form phosphor powder. As the raw materials of the phosphor,oxides, nitrates and hydroxides mainly are used. However, organic metalcompounds containing elements such as Ba, Sr, Mg, Al, Eu, Mo and W,e.g., metal alkoxide and acetylacetone may be used so as to manufacturethe phosphor. Moreover, by annealing the afore-mentioned reducedphosphor in an oxidizing atmosphere, a phosphor with reduceddeterioration due to vacuum ultraviolet light (VUV) can be obtained.

(3) Green Phosphor (Zn_(2−x)SiO₄: Mn_(x))

Firstly, in a step of manufacturing a mixture solution, zinc nitrateZn(NO₃)₂, silicon nitrate Si(NO₃)₂ and manganese nitrate Mn(NO₃)₂ as rawmaterials are mixed so as to have a molar ratio of 2−X:1:X(0.01≦X≦0.10). Thereafter, this mixture solution is sprayed from anozzle into an oven heated at 1500° C. while applying ultrasonic wavethereto, whereby the green phosphor is manufactured.

(4) Green Phosphor (Y_(1−x)BO₃: Tb_(x))

Firstly, in a step of manufacturing a mixture solution, yttrium nitrateY₂(NO₃)₃, boric acid H₃BO₃ and terbium nitrate Tb(NO₃)₃ as raw materialsare mixed so as to have a molar ratio of 1−X:1:X (0.01≦X≦0.10). This isdissolved in ion-exchanged water so as to manufacture the mixturesolution.

Next, in a step of hydration, a basic water solution (e.g., ammoniawater solution) is dropped into this mixture solution, whereby a hydrateis formed. Thereafter, in a step of hydrothermal synthesis, this hydrateand ion-exchanged water are poured into a capsule having the corrosionresistance and the heat resistance, made of gold or platinum, forexample, which is then subjected to hydrothermal synthesis (for 2 to 20hours) in a high pressure container at a predetermined temperature (100to 300° C.) and under a predetermined pressure (0.2 MPa to 10 MPa) usingan apparatus such as an autoclave.

Thereafter, this is dried, so that a desired Y_(1−x)BO₃: Tb_(x) can beobtained. With this hydrothermal synthesis step, the obtained phosphorhas a particle diameter of about 0.1 μm to 2.0 μm and has a sphericalshape.

Next, this powder is annealed in the air at 800° C. to 1100° C.,followed by screening out, thus obtaining the green phosphor.

(5) Red Phosphor ((Y, Gd)_(1−x)BO₃: Eu_(x))

In a step of manufacturing a mixture solution, yttrium nitrate Y₂(NO₃)₃,gadolinium nitrate Gd₂(NO₃)₃, boric acid H₃BO₃ and europium nitrateEu₂(NO₃)₃ as raw materials are mixed so as to have a molar ratio of1−X:2:X (0.05≦X≦0.20) and a ratio between Y and Gd of 65:35. Next, thisis heat-treated in the air at 1200° C. to 1350° C. for 2 hours, followedby screening out, thus obtaining the red phosphor.

(6) Red Phosphor (Y_(2−x)O₃: Eu_(x))

In a step of manufacturing a mixture solution, yttrium nitrate Y₂(NO₃)₂and europium nitrate Eu(NO₃)₂ as raw materials are mixed, which isdissolved in ion-exchanged water so as to have a molar ratio of 2-X: X(0.05≦X≦0.30), thus manufacturing a mixture solution. Next, in a step ofhydration, a basic water solution, e.g., ammonia water solution, isdropped into this water solution, whereby a hydrate is formed.

Thereafter, in a step of hydrothermal synthesis, this hydrate andion-exchanged water are poured into a container having the corrosionresistance and the heat resistance, made of gold or platinum, forexample, which is then subjected to hydrothermal synthesis (for 3 to 12hours) in a high pressure container at a temperature of 100 to 300° C.and under a pressure of 0.2 MPa to 10 MPa using an apparatus such as anautoclave. Thereafter, the thus obtained compound is dried, so that adesired Y_(2−x)O₃ Eu_(x) can be obtained. Next, this phosphor isannealed in the air at 1300° C. to 1400° C. for 2 hours, followed byscreening out, thus obtaining the red phosphor. With this hydrothermalsynthesis step, the obtained phosphor has a particle diameter of about0.1 μm to 2.0 μm and has a spherical shape. This particle diameter andthe shape are suitable for the formation of a phosphor layer withexcellent luminescent characteristics.

Then, in order to evaluate the performances of the plasma display deviceof the present invention, samples were manufactured in accordance withthe above embodiment, and performance evaluation examinations wereconducted for these samples. The experimental results will be describedbelow.

The manufactured respective plasma display devices were 42 inch in size(rib pitch of 150 μm required by HD-TVs), where the thickness of thedielectric glass layer was 20 μm, the thickness of the MgO protectivelayer was 0.5 μm and the distance between the display electrodes and thedisplay scanning electrodes was 0.08 mm. A discharge gas with which thedischarge space was filled was a mixed gas of neon as a main gas with 7vol % xenon gas mixed thereto, the discharge gas being filled at apredetermined discharge gas pressure.

For the respective blue phosphor particles used in the plasma displaydevices of samples 1 to 10, phosphors were used in which Mg, Al and Baions making up the phosphors are substituted with ions. Tables 2 to 3show the respective conditions for synthesis. TABLE 2 Amount of elementsSample Amount of Eu Manufacturing with which Al, Mg No. x,y method andBa are substituted Blue phosphors (Ba_(1 ·x)MgAl₁₀O₁₇:Eu_(x)) 1 x = 003Hydrothermal W 0.05 synthesis 2 x = 0.05 Solid phase reaction W 0.01(flux method) 3 x = 0.1 Solid phase reaction Mo 0.03 (flux method) 4 x =0.2 Water solution Mo 3.0 Blue phosphors (Ba_(1·x·y)SryMgAl₁₀O₁₇:Eu_(x))5 x = 0.03, y = 0.1 Solid phase reaction W 1.0 (flux method) 6 x = 0.1,y = 0.3 Hydrothermal W 0.001 synthesis 7 x = 0.03, y = 0.1 Spraying Mo0.02 8 x = 0.1, y = 0.5 Solid phase reaction Mo 1.0 9 x = 0.2, y = 0.3Solid phase reaction Mo 1.0,W 0.5 10 x = 0.1, y = 0.5 Solid phasereaction Mo 0.1,W 0.05 *11 x = 0.1, y = 0.5 Solid phase reaction None(Remark) *11 shows comparative example.

TABLE 3 Green phosphors ((Y, Gd)_(1−x)BO₃:Eu_(x)) (Zn_(2−x)SiO₄: Mn_(x))Sample Amount of Eu, Manufacturing Manufacturing No. x methods Amount ofMn, x methods Red phosphors 1 X = 1 Solid phase X = 0.01 Sprayingreaction 2 X = 0.2 Spraying X = 0.02 Hydrothermal synthesis 3 X = 0.3Water solution X = 0.05 Solid phase reaction 4 x = 0.15 Hydrothermal X =0.1 Solid phase synthesis reaction Green phosphors (mixture of(Zn_(2−x)SiO₄: Mn_(x)) (Y_(2−x)O₃:Eu_(x)) and(Y_(1−x)BO₃:Tb_(x)), Redphosphors ratio 1:1) 5 x = 0.01 Hydrothermal X = 0.01 Hydrothermalsynthesis synthesis 6 x = 0.1 Spraying X = 0.02 Spraying 7 x = 0.15Water solution X = 0.05 Solid phase reaction 8 x = 0.2 Solid phase X =0.1 Solid phase reaction reaction 9 x = 0.2 Solid phase X = 0.1 Solidphase reaction reaction 10 x = 0.15 Water solution X = 0.01 Solid phasereaction *11 x = 0.15 Water solution Zn₂SiO₄:Mn only Solid phase x =0.05 reaction(Remark)*11 shows comparative example.

Samples 1 to 4 included the combination of (Y, Gd)_(1·x)BO₃: Eu_(x) usedas the red phosphors, Zn_(2·x)SiO₄: Mn_(x) used as the green phosphorsand Ba_(1·x)MgAl₁₀O₁₇:Eu_(x) used as the blue phosphors. The methods forsynthesizing the phosphors, the substitution ratios of Eu and Mnfunctioning as luminescent center, i.e., the substitution ratios of Euelements with reference to Y, Ba elements and the substitution ratios ofMn with reference to Zn elements and the types and the amounts of ions(elements) with which Mg, Al and Ba are substituted were changed asshown in Tables 2 to 3.

Samples 5 to 10 included the combination of Y_(2·x)O₃: Eu_(x) used asthe red phosphors, the mixture of Zn_(2·x)SiO₄: Mn_(x) and Y_(1·x)BO₃:Tb_(x) used as the green phosphors and Ba_(1·x·y)Sr_(y)MgAl₁₀O₁₇: Eu_(x)used as the blue phosphors. Similarly to the above, the conditions forthe methods of synthesizing the phosphors and the substitution ratios ofthe luminescent center and the types and the amounts of ions (elements)with which Mg, Al and Ba making up the blue phosphors are substitutedwere changed as shown in Tables 2 to 3.

Furthermore, the phosphor inks used for the formation of the phosphorlayers were manufactured by using the respective phosphor particlesshown in Tables 2 to 3 and mixing the phosphors, a resin, a solvent anda dispersing agent. The viscosity of the phosphor inks in this step (25°C.) could be kept within a range of 1500 CP and 30000 CP in all samples.When observing the thus formed phosphor layers, the phosphor inks wereapplied uniformly on the walls of the barrier ribs in all samples.Furthermore, in the respective samples, the phosphor particles used forthe phosphor layers in the respective colors had the average particlediameter of 0.1 μm to 3.0 μm and the maximum particle diameter of 8 μmor less.

The comparative sample 11 is as follows: sample 11 used the conventionalphosphor particles in which no special treatment had been conducted forthe phosphor particles in the respective colors.

(Experiment 1)

As for the thus manufactured samples 1 to 10 and the comparative sample11, the brightness for the respective colors after the phosphor bakingstep (520° C., 20 min.) in the rear panel manufacturing process wasmeasured. Then, after the panel bonding step (sealing step at 450° C.for 20 min.) in the panel manufacturing process, the rates of change(deterioration) in the brightness for the respective phosphors weremeasured.

(Experiment 2)

The brightness of the illumination states of a panel for the respectivecolors and the rates of change (deterioration) in the brightness weremeasured as follows: discharge sustaining pulses with a voltage of 180 Vand a frequency of 100 kHz were applied to a plasma display devicecontinuously for 1000 hours life test) and the panel brightness beforeand after the test was measured. From the measurement results, the rateof change (deterioration) in brightness ([{brightness after thetest—brightness before the test}/brightness before the test]×100) wasdetermined. Address errors during the address discharge were judged fromthe observation of an image so as to check flickering. When flickeringoccurred even at one point, this was judged as an error. Furthermore,the brightness distribution, uneven color and shift in color of thepanel were determined by measuring the brightness of a white image by aluminance meter and were judged from the overall distribution and byvisual inspection.

Table 4 shows the results of the brightness, the rate of change(deterioration) in brightness for the respective colors and the visualinspection of the address errors and uneven color for Experiments 1 and2.

(Experiment 3)

The phosphors in all colors were recovered from samples 1 to 10 andcomparative sample 11, and the amounts of the absorbed gas of thesephosphors were measured using a TDS analyzer (thermal desorptionspectrometry apparatus), where outgassing amounts of water, CO₂ andhydrocarbon gas at 100° C. to 600° C. were measured. Next, assuming thatthe total outgassing amount of water, CO₂ and hydrocarbon gas (massnumber 40 or more) of sample 1 was 1, the relative amounts of samples 2to 10 and the comparative sample 11 were measured so as to measure therelative values of the gas amounts contained in the phosphors. Table 4shows these results also. TABLE 4 Uneven color and Presence shift inBrightness of Rate of of color phosphors change address during Rate ofin errors illumination deterioration¹⁾ brightness²⁾ during state ofRelative Sample (%) (%) address white full ratio of No. Blue Red GreenBlue Red Green discharge display adsorbate³⁾ 1 −0.8 −1.2 −3.0 −0.7 −1.0−2.8 No No 1 2 −0.5 −1.2 −3.1 −0.5 −0.9 −2.5 No No 0.9 3 −1.5 −1.3 −3.5−1.0 −1.1 −2.9 No No 1.5 4 −1.0 −1.4 −3.9 −0.8 −0.8 −2.7 No No 1 5 −1.2−1.5 −3.6 −1.1 −1.0 −2.5 No No 0.8 6 −1.1 −1.3 −3.3 −0.9 −0.8 −2.1 No No0.7 7 −1.5 −1.4 −3.8 −1.2 −1.2 −2.8 No No 1.1 8 −0.8 −1.3 −3.5 −0.4 −0.6−2.9 No No 1.4 9 −0.8 −1.2 −2.8 −0.3 −0.6 −1.8 No No 0.6 10 −0.6 −1.1−2.9 −0.2 −0.5 −1.9 No No 0.7 *11⁴⁾ −21.5 −2.1 −13.2 −20.5 −1.8 −10.3Yes Yes 10.5(Remark¹⁾ Rates of deterioration in brightness (%) of phosphors afterthe sealing step (450° C.) in the panel bonding process with referenceto the brightness after the phosphor baking process are shown.(Remark²⁾ Rates of change in brightness (%) of the panels after theapplication of discharge sustaining pulses at 180 V and 100 kHz for 1000hours are shown.(Remark³⁾ The total amounts of water, CO₂ and hydrocarbon gas adsorbedto the phosphors in the panels are represented by relative ratiosassuming that the total amount of sample 1 was 1.(Remark⁴⁾*11 shows comparative example.

As shown in Table 4, sample 11 in which the substitution treatment withions had not been conducted on the blue phosphor, showed significantdeterioration in brightness during the respective steps, in particular,in blue and green brightness. As for blue, a reduction in brightness of21.5% occurred during the sealing step after the phosphor baking stepand a reduction in brightness of 20.5% occurred during the life test at180 V and 100 Hz. As for green, a reduction in brightness of 13.2%occurred during the panel bonding step and a reduction in brightness of10.3% occurred during the life test at 180 V and 100 kHz. In accordancewith these changes in brightness, the degree of uneven color and shiftin color also increased. On the other hand, in all of samples 1 to 10,the rate of change for blue was 2% or less after the panel bonding stepand the life test, and that for green also was 4% or less. Moreover,they were free from address errors, uneven color and shift in color ofthe panels.

This results from the substitution of Mg, Al and Ba ions (elements)making up the blue phosphor with the specific ions or elements (Nb, Ta,W, B), which allows a significant decrease in oxygen defects in the bluephosphor (especially, oxygen defects in the vicinity of Ba-O).Therefore, water, CO₂ and hydrocarbon gas and the like that aredischarged from this blue phosphor are decreased considerably, and theamount of outgassing from the blue phosphor during the panel sealingprocess can be reduced, which can exert favorable effects not only onthe blue itself but also on the adjacent green and red phosphors andMgO. Especially, samples 4, 6 and 8 whose blue phosphors were annealedin an oxidizing atmosphere had reduced rates of change in brightnessafter the discharge sustaining pulse test at 180 V and 100 kHz becauseoxygen defects thereof could be reduced.

Furthermore, as shown in Tables 2 to 3, it was found that the impuritygas amounts of the phosphors of the panels in samples 1 to 10 using theblue phosphors whose Mg, Al and Ba were substituted with the specificions or elements (Nb, Ta, W, B) were smaller than those of comparativeexample 11. Conceivably, such a reduced amount of impurity gascontributes to less deterioration in brightness for blue and green.Therefore, with the panel using blue phosphor whose Mg, Al and Ba aresubstituted with the specific ions or elements (Nb, Ta, W, B), addresserrors, uneven color and shift in color can be alleviated.

The conventional blue phosphors had an increased degree of deteriorationduring the respective steps as compared with the blue phosphor of thepresent invention and tended to decrease in color temperature of whitewhen light in three colors was emitted concurrently. To cope with this,the color temperature of a white image in the conventional plasmadisplay device has been corrected by decreasing the brightness of thecell for phosphors other than blue (i.e., red and green phosphors) bymeans of a circuit. However, the use of the phosphor particles includingblue phosphor in which a part of Mg, Al and Ba ions constituting theblue phosphor is substituted with the specific ions or elements (Nb, Ta,W, B) allows the brightness of blue to be enhanced. Furthermore, suchphosphor particles can reduce deterioration during the panelmanufacturing process and deterioration in green also can be reduced.Therefore, there is no need to decrease the brightness of cells in othercolors intentionally, which means that there is no need to decrease thebrightness of cells in all colors intentionally. Therefore, thebrightness of the cells in all colors can be utilized fully, so that thebrightness of the plasma display device can be increased while keeping ahigh color temperature state for a white image.

Note here that the above blue phosphor can be applied to a fluorescentlamp that emits light by exciting with the same ultraviolet rays. Insuch a case, the conventional blue phosphor particles applied on aninner wall of the fluorescent lamp may be replaced by a phosphor layerincluding blue phosphor in which Mg, Al and Ba ions making up the bluephosphor particles are substituted with the specific ions (Nb, Ta, W,B). In this way, when the above blue phosphor is applied to afluorescent lamp and a backlight for liquid crystal displays, higherbrightness and reduced deterioration in brightness can be realized ascompared with the conventional one.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. An alkaline-earth metal aluminate phosphor containing an element M(where M denotes at least one type of element selected from the groupconsisting of Nb, Ta, W and B), wherein a concentration of M in thevicinity of a surface of phosphor particles constituting the phosphor ishigher than an average concentration of M in the phosphor particles as awhole.
 2. The phosphor according to claim 1, wherein Eu is included asthe luminescent center.
 3. The phosphor according to claim 1, whereinthe alkaline-earth metal aluminate comprises an alkaline-earth metalaluminate represented by a general formula of xBaO. (1·x)SrO.zMgO.5Al₂O₃(0.60≦x≦1.00, 1.00≦z≦1.05), and 0.40 to 1.70 mol % of Eu in terms of Euand 0.04 to 0.80 mol % of W in terms of W are included with reference tothe alkaline-earth metal aluminate.
 4. The phosphor according to claim1, wherein the concentration of M in the vicinity of the surface of thephosphor particles ranges from 0.30 to 9.00 mol %.
 5. The phosphoraccording to claim 2, wherein a concentration of Eu in the vicinity ofthe surface of the phosphor particles is higher than an averageconcentration of Eu in the phosphor particles as a whole, and a divalentEu ratio (a ratio of divalent Eu elements to all of the Eu elements) inthe vicinity of the surface of the phosphor particles is lower than anaverage divalent Eu ratio in the phosphor particles as a whole.
 6. Thephosphor according to claim 5, wherein the divalent Eu ratio in thevicinity of the surface of the phosphor particles ranges from 5 to 50mol %, and the average divalent Eu ratio in the phosphor particles as awhole ranges from 60 to 95 mol %.
 7. The phosphor according to claim 5,wherein the divalent Eu ratio in the vicinity of the surface of thephosphor particles ranges from 5 to 15 mol %, and the average divalentEu ratio in the phosphor particles as a whole ranges from 60 to 80 mol%.
 8. The phosphor according to claim 1, wherein the phosphor is a bluephosphor having a crystal structure of Ba_(1·x)MgAl₁₀O₁₇: Eu_(x) orBa_(1−x−y)Sr_(y)MgAl₁₀O₁₇: Eu_(x) (where 0.03≦X≦0.20, 0.1≦Y≦0.5).
 9. Thephosphor according to claim 8, wherein the blue phosphor comprisesparticles.
 10. The phosphor according to claim 1, wherein theconcentration of M in the vicinity of a surface of the phosphorparticles is twice or higher than the average concentration of M in thephosphor particles as a whole.
 11. The phosphor according to claim 10,wherein the concentration of M in the vicinity of a surface of thephosphor particles is three times or higher than the averageconcentration of M in the phosphor particles as a whole.
 12. Thephosphor according to claim 1, wherein the vicinity of the surface ofthe phosphor particles is a range of 50 nm or less from the surface ofthe phosphor particles.
 13. The phosphor according to claim 12, whereinthe vicinity of the surface of the phosphor particles is an averagevalue in a region of 10 nm or less from the surface of the phosphorparticles.
 14. The phosphor according to claim 9, an average content ofthe M element in the blue phosphor is within a range of 0.001 to 3.0 mol%.
 15. The phosphor according to claim 9, wherein an average particlediameter of the phosphor particles is within a range of 0.05 μm to 3.0μm, inclusive.
 16. The phosphor according to claim 15, wherein theaverage particle diameter of the phosphor particles is within a range of0.1 μm to 2.0 μm, inclusive.
 17. The phosphor according to claim 15,wherein the phosphor particles have a particle size distribution suchthat a maximum particle diameter is four times or less the averageparticle diameter and a minimum particle diameter is one fourth or morethe average particle diameter.
 18. The phosphor according to claim 1,wherein the phosphor layers are formed by mixing phosphor particles witha binder so as to make a paste and by applying the paste onto a surfaceof the discharge cells, followed by baking.
 19. A plasma display device,comprising a plasma display panel in which a plurality of dischargecells in one color or in a plurality of colors are arranged and phosphorlayers are arranged so as to correspond to the discharge cells in colorsand in which light is emitted by exciting the phosphor layers withultraviolet rays, wherein the phosphor layers comprise blue phosphor,the blue phosphor being an alkaline-earth metal aluminate phosphorcontaining an element M (where M denotes at least one type of elementselected from the group consisting of Nb, Ta, W and B), and aconcentration of M in the vicinity of a surface of phosphor particlesconstituting the phosphor is higher than an average concentration of Min the phosphor particles as a whole.
 20. The plasma display deviceaccording to claim 19, wherein a thickness of the phosphor layers iswithin a range of 8 times to 25 times an average particle diameter ofphosphor particles, inclusive.